Many heated structures require a high degree of uniformity and heat distribution to achieve uniform results and performance of the structure. As heat from the heated structure is taken away, heat distribution becomes transiently non-uniform. Such a transient non-uniformity of temperature across the structure or on a heated surface may result in unacceptable performance of the structure. For example, heat distribution on the surface of a fuser roll in a photocopier can be disturbed as a printing media is passed over a part of a surface of the fuser roll. If printing on one size medium is followed immediately by printing of a different size medium, the second medium will receive non-uniform heat applied thereto from the fuser roll. Since proper fusing of fusible inks is a function of heat, residence time and pressure, if the pressure and residence time are the same but the heat applied varies from one part of the medium to another part of the medium, non-uniform fusing can occur. Under fused inks can cause smearing, offset and other unacceptable conditions.
A simple solution to the non-uniformity of heat distribution is to allow a sufficient time lag between operations for the structure to reheat such that the heat is distributed substantially uniformly on the critical region. However, such delay itself can be unacceptable. In photocopiers and printers, increased speed and performance are highly sought after. Thus, delaying a subsequent copying function for a different size medium following a first size medium can require unacceptable delay in a high-speed office machine. As heat is applied, non-uniformity can remain if all areas are heated equally until a maximum temperature is reached and distributed evenly.
It is known to use heat pipes to achieve improved heat distribution uniformity. However, the heat response time of a heat pipe depends on the outer surface material, and it is often difficult to maintain a very thin outer surface on a heat pipe. The heat pipe requires a liquid or vapor within the heat pipe, and the assembly is somewhat cumbersome to install and expensive to manufacture.
What is needed in the art is an improved construction for a heat-equalizing device to maintain heat equilibrium of a heated structure, and to minimize transient temperature differences within critical areas of the heated structure.